A special purpose rotational viscometer is used to determine the response of human platelets to shear stress. The objective of the proposed work is to study morphological, biochemical, and functional changes in platelets subjected to graded shear stress fields for various times, and to the combination of shear stress and foreign surface interaction. Studies are being carried out in the presence of certain antiplatelet agents including acetylsalicylic acid and various prostaglandins. The results will contribute to our understanding of the fluid mechanics or engineering mechanics of cell damage, cell stimulation, and thrombus formation, and may help elucidate the role of the platelet in arterial disease.